I need help with this, I think the first two are right but if not correct me, anyway I need help with C and D D is: "use substitution to solve the system for X. show your work"​

1. the following set of data represents the number of waiting times in minutes from a random sample of 30 customers waiting for service at a department store. 4 5 7 10 11 11 12 12 13 15 15 17 17 17 17 17 18 20 20 21 22 22 23 24 25 27 27 31 31 32 a. determine the number of classes and class interval.

Can someone me i’m confused. will give brainliest and a whole bunch of points

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years